In a coordinated multipoint transmission and reception (CoMP) technology, coordinated transmission between multiple cells is used, which effectively solves a problem of interference of cell edges, thereby improving throughput of the cell edges and a system and broadening high-speed transmission coverage. CoMP includes downlink CoMP transmission and uplink CoMP reception. In the uplink CoMP reception, user data is jointly received by multiple cells so as to improve user throughput of the cell edges; and the downlink CoMP transmission may be divided into joint processing (JP) and coordinated scheduling/beam forming (CS/CB) according to whether service data can be obtained on multiple coordinated points. The JP may obtain a transmission gain, and the CS/CB can reduce interference between the cells.
To support different CoMP transmission manners, it is required to obtain user channel state information in different forms. There are three obtaining types: explicit feedback, implicit feedback, and channel estimation based on a sounding reference signal (SRS). The explicit feedback refers to that a terminal does not perform preprocessing on user channel state information, and feeds back information such as a channel coefficient. The implicit feedback refers to that a terminal performs, in a given condition, certain preprocessing on user channel state information and then feeds back the information to a base station, such as precoding matrix indicator information and channel rank indicator information. In a time division duplexing (TDD) system, channel reciprocity is further used to obtain equivalent downlink user channel state information according to an SRS sent by a terminal.
To adapt to increasingly fierce competition and a continuously growing throughput requirement, a coverage area of a radio base station becomes smaller and smaller. Deployment of a small base station is flexible. However, because each small base station works independently, a JP gain cannot be obtained. Recently, a radio access network system based on a cloud computing technology has attracted common attention of the industrial circle. In this architecture, baseband processing units (BBU) of multiple base stations are centralized to support large-scale JP, so as to improve system capacity, and system cost is reduced at the same time using resource statistical multiplexing. In the large-scale JP, it is required to return data of each remote radio frequency unit (RRU) from a long distance to a BBU resource pool. At present, a BBU, acting as a baseband processing unit, and an RRU are interconnected through an interface such as a common public radio interface (CPRI), and a data transmission rate on the CPRI interface increases linearly with the number of antennas and a system bandwidth. For example, a bandwidth of a long term evolution (LTE) system is 20 megahertz (MHz), 8 antennas are used, and transmission traffic reaches 10 gigabits per second (Gbps). Such a high transmission bandwidth requirement brings a large challenge to an existing transmission network of an access layer, and an operator without abundant optical fiber resources has difficulties in deployment. To lower the transmission bandwidth requirement on the CPRI, multiple technologies are developed. However, a technology which not only can reduce the transmission bandwidth on the CPRI but also can obtain a system capacity gain at the same time is still in need.